1. Field of the Invention
The present invention relates to an object, a method, or a manufacturing method. In addition, the present invention relates to a process, a machine, manufacture, or a composition of matter. In particular, one embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a memory device, a driving method thereof, or a manufacturing method thereof.
Note that in this specification, a semiconductor device means a circuit including a semiconductor element (e.g., a transistor or a diode) and a device including the circuit. The semiconductor device also means any device that can function by utilizing semiconductor characteristics. For example, an integrated circuit, a chip including an integrated circuit, a display device, a light-emitting device, a lighting device, an electronic device, and the like include a semiconductor device in some cases.
2. Description of the Related Art
A transistor is applied to a wide variety of electronic devices such as an integrated circuit (IC) or an image display device (display device). As materials of a semiconductor that can be used in the transistor, silicon-based semiconductor materials have been widely known, but oxide semiconductors have been attracting attention as alternative materials.
For example, a transistor including an amorphous oxide semiconductor layer containing indium (In), gallium (Ga), and zinc (Zn) is disclosed in Patent Document 1.
Techniques for improving carrier mobility by employing a stacked structure of an oxide semiconductor layer are disclosed in Patent Documents 2 and 3.
Further, as one of means of downsizing and obtaining narrowed bezel of an active matrix display device, it has been known to form a driver circuit and a pixel portion on one substrate. Pixel circuits of the display device can be formed with either an n-channel transistor or a p-channel transistor. Accordingly, it is preferable to design a driver circuit with a single conductivity type transistor instead of using a CMOS circuit in order to manufacture a display device having a narrow bezel width with reduced number of manufacturing steps and manufacturing cost.
Main circuits of a driver circuit in a display device are shift registers. For example, Patent Documents 4 and 5 each disclose a shift register that includes a transistor using an oxide semiconductor layer.